Isocyanate compositions for blown polyurethane foams

ABSTRACT

Rigid polyurethane foams are prepared from an isocyanate composition containing diphenylmethane diisocyanate, three ring oligomers of polyphenylene polymethylene polyisocyanate and higher homologues of polyphenylene polymethylene polyisocyanate.

[0001] The present invention is directed to processes for the productionof rigid polyurethane foams and reaction systems for use therein. Morespecifically, the present invention is directed to processes for theproduction of rigid polyurethane foam utilizing a specificpolyisocyanate composition, an isocyanate-reactive composition andhydrofluorocarbon or hydrocarbon blowing agents.

[0002] Rigid polyurethane foams have many known uses, such as inbuilding materials and thermal insulation. Such foams are known to havesuperior structural properties, outstanding initial and long termthermal insulation and good fire retardation properties.

[0003] Rigid polyurethane foams have conventionally been prepared byreacting appropriate polyisocyanate and isocyanate-reactive compositionsin the presence of a suitable blowing agent. With regard to blowingagents, chlorofluorocarbons (CFC's) such as CFC-11 (CCl₃F) and CFC-12(CCl₂F₂) have been used most extensively as they have been shown toproduce foams having good thermal insulation properties, lowflammability and excellent dimensional stability. However, in spite ofthese advantages, CFC's have fallen into disfavor, as they have beenassociated with the depletion of ozone in the earth's atmosphere, aswell as possible global warming potential. Accordingly, the use of CFC'shas been severely restricted.

[0004] Hydrochlorofluorocarbons (HCFC's) such as HCFC 141b (CCl₂FCH₃)and HCFC22(CHClF₂) have become a widely used interim solution. However,HCFC's have also been shown to cause a similar depletion of ozone in theearth's atmosphere and accordingly, their use has also come underscrutiny. In fact, the widespread production and use of HCFCs isscheduled to end shortly.

[0005] Therefore, there has existed a need to develop processes for theformation of rigid polyurethane foams which utilize blowing agentshaving a zero ozone depletion potential and which still provide foamshaving excellent thermal insulation properties and dimensionalstability.

[0006] A class of materials which have been investigated as such blowingagents include various hydrocarbons such as n-pentane, n-butane andcyclopentane. The use of such materials is well-known and disclosed,e.g., in U.S. Pat. Nos. 5,096,933, 5,444,101, 5,182,309, 5,367,000 and5,387,618. However, known methods for producing foams with such blowingagents and reaction systems used in such methods have not been found toproduce rigid polyurethane foams having commercially attractive physicalproperties at densities which are sufficiently low to make their usefeasible. In short, the properties associated with such hydrocarbonblown foams have generally been inferior to CFC and HCFC blown foams.

[0007] Attention has also turned to the use of hydrofluorocarbons(HFC's) including 1,1,1,3,3-pentafluoropropane (HFC 245fa);1,1,1,3,3-pentafluorobutane (HFC 365mfc); 1,1,1,2-tetrafluoroethane (HFC134a); and 1,1-difluoroethane (HFC 152a). The use of such materials asblowing agents for rigid polyurethane foams is disclosed, e.g., in U.S.Pat. Nos. 5,496,866; 5,461,084; 4,997,706; 5,430,071; and 5,444,101.However, as with hydrocarbons, attempts to produce rigid foams with suchmaterials have generally not resulted in foams having structural,thermal and thermal properties comparable to those attained using CFC-11as the blowing agent.

[0008] The majority of attempts to solve this problem have centeredaround the blending of different hydrofluorocarbons, hydrocarbons or theblending of hydrocarbons with hydrofluorocarbons and/or other blowingagents. Such attempts have met with limited success.

[0009] Accordingly, there remains a need for a process for theproduction of rigid polyurethane foam which utilizes hydrofluorocarbonor hydrocarbon blowing agents and which provides foams having excellentphysical properties.

[0010] This objective is obtained by the present invention whichutilizes polymeric polyisocyanates of a specific composition in theprocess for the production of rigid polyurethane foam withhydrofluorocarbon or hydrocarbon blowing agents. The present inventionprovides foams having improved physical and thermal insulationproperties.

[0011] The present invention is directed to a process for making rigidpolyurethane foams comprising reacting:

[0012] (1) a polyphenylene polymethylene polyisocyanate composition;

[0013] (2) an isocyanate-reactive composition containing a plurality ofisocyanate-reactive groups which are useful in the preparation of rigidpolyurethane or urethane-modified polyisocyanurate foams;

[0014] (3) a hydrofluorocarbon or hydrocarbon blowing agent;

[0015] (4) optionally, water or other carbon dioxide evolving compounds,and

[0016] wherein said polyphenylene polymethylene polyisocyanate comprises

[0017] (a) a 15 to 42 percent by weight, based on 100% of thepolyisocyanate component (1), of diphenylmethane diisocyanate;

[0018] (b) 3-ring oligomers of polyphenylene polymethylenepolyisocyanate (henceforth referred as triisocyanate) in an amount suchthat the ratio of diisocyanate to triisocyanate is between about 0.2 toabout 1.8; and

[0019] (c) the remainder being higher homologues of polyphenylenepolymethylene polyisocyanate.

[0020] The present invention is further directed to reaction systemuseful for the preparation of rigid polyurethane foams comprising

[0021] (1) a polyphenylene polymethylene polyisocyanate composition;

[0022] (2) an isocyanate-reactive composition containing a plurality ofisocyanate-reactive groups which are useful in the preparation of rigidpolyurethane or urethane-modified polyisocyanurate foams;

[0023] (3) a hydrofluorocarbon or hydrocarbon blowing agent;

[0024] (4) optionally, water or other carbon dioxide evolving compounds,and

[0025] wherein said polyphenylene polymethylene polyisocyanatecomprises:

[0026] (a) a 15 to 42 percent by weight, based on 100% of thepolyisocyanate component (1), of diphenylmethane diisocyanate;

[0027] (b) 3-ring oligomers of polyphenylene polymethylenepolyisocyanate (henceforth referred as triisocyanate) in an amount suchthat the ratio of diisocyanate to triisocyanate is between about 0.2 toabout 1.8; and

[0028] (c) the remainder being higher homologues of polyphenylenepolymethylene polyisocyanate.

[0029] The polyphenylene polymethylene polyisocyanates used in thepresent invention are those of Formula I

[0030] 3-ring oligomers of component 1(b) are those represented byFormula I where n=1. The higher homologues of component 1(c) are thoserepresented by Formula I where n>1.

[0031] The polyphenylene polymethylene polyisocyanate composition (1)used in the present invention comprises about 15 to about 42 percent,preferably about 20 to about 40 percent and more preferably 24 to about38 percent by weight, based upon 100 percent of the polyisocyanatecomponent, of diphenylmethane diisocyanates. Diphenylmethanediisocyanate in the form of its 2,2′, 2,4′ and 4,4′ isomers and mixturesthereof may be used as in the present invention. Any variation of the2,2′, 2,4′ and 4,4′ isomers may be utilized.

[0032] The polyphenylene polymethylene polyisocyanate composition (1)further comprises the triisocyanate component in an amount such that theratio of diisocyanate to triisocyanate is between 0.2 to 1.8 andpreferably between about 0.33 to about 1.8. Thus, the actualtriisocyanate content is determined based upon the amount ofdiphenylmethane diisocyanate in the polyphenylene polymethylenecomposition (1) utilizing the above-stated ratio. The amount is on apercent by weight basis based on 100 percent by weight of the totalpolyisocyanate composition.

[0033] For purposes of clarification, if the amount of diphenylmethanediisocyanate in a given polyphenylene polymethylene polyisocyanatecomposition is 30 percent and the ratio of diisocyanate to triisocyanateis 1.5, the amount of triisocyanate which must be incorporated into thepolyphenylene polymethylene polyisocyanate composition would then be 20percent by weight based upon 100 percent by weight of the totalcomposition. As used herein, the term “triisocyanate” means all isomersof 3-ring oligomers of polyphenylene polymethylene polyisocyanate (i.e.,n=1 in Formula I) containing three phenyl, two methyl and threeisocyanate groups. Seven possible isomers of triisocyanate are describedin “Chemistry and Technology of Isocyanates” by Henri Ulrich, John Wiley& Sons Inc., p. 388 (1996).

[0034] The remainder of the polyphenylene polymethylene polyisocyanatecomposition comprises higher homologues of polyphenylene polymethylenepolyisocyanate. The higher homologues include all of those which arehigher than tri, i.e., tetraisocyanate, heptaisocyanate, hexaisocyanate,etc (i.e., n>1 in Structure 1). Suitable higher homologues are describedin “The Polyurethanes Book”, edited by George Woods, John Wiley & SonsPublisher (1987). The amount of higher homologues contained within thepolyphenylene polymethylene polyisocyanate composition is generallyabout 10 to about 77 and preferably about 19 to about 69 percent, basedon 100 percent by weight of the total composition.

[0035] The higher homologue component (c) may further comprise higherfunctionality isocyanates modified with various groups containing estergroups, urea groups, biuret groups, allophanate groups, carbodiimidegroups, isocyanurate groups, uretdione groups and urethane groups. Suchmodified isocyanates and methods for the preparation are known in theart.

[0036] The polyphenylene polymethylene polyisocyanate composition (1) isused in an amount of about 35 to about 70 of the total reaction system.

[0037] The polyphenylene polymethylene polyisocyanate composition (1)may be prepared by methods known to those skilled in the art. Suitablemethods are disclosed, e.g., in “Chemistry and Technology ofIsocyanates” Ulrich, John Wiley & Sons Inc. (1996). In general, thepolyphenylene polymethylene polyisocyanate compositions are prepared bythe reaction of aniline with formaldehyde under acidic conditions toform amines. This is followed by phosgenation and thermal cleavage ofthe resulting material into a mixture of isocyanate homologues. Theamount of diphenylmethane diisocyanate, triisocyanate and higherhomologues in the composition can be manipulated by adjusting theaniline to formaldehyde ratio and/or the reaction conditions. Forexample, a higher aniline to formaldehyde ratio results in apolyphenylene polymethylene polyamine which contains higher amounts ofthe diphenylmethane diamine component and the triamine component and acorrespondingly lower yield of the higher homologue component.Therefore, phosgenation and thermal cleavage of the resultingpolyphenylene polymethylene polyamine yields a polyphenylenepolymethylene polyisocyanate product which contains higher amounts ofthe diphenylmethane diisocyanate and the triisocyanate and lower amountsof the higher homologues of isocyanate. Moreover, the composition of thepolyphenylene polymethylene polyisocyanate component which contains canalso be controlled by partial fractionation to separate diphenylmethanediisocyanate along with a variety of isocyanate modified reactionroutes.

[0038] The isocyanate-reactive compositions (2) useful in the presentinvention include any of those known to those skilled in the art to beuseful for the preparation of rigid polyurethane foams. Examples ofsuitable isocyanate-reactive compositions having a plurality ofisocyanate-reactive groups include polyether polyols, polyester polyolsand mixtures thereof having average hydroxyl numbers of from about 20 toabout 1000 and preferably about 50 to 700 KOH/g and hydroxylfunctionalities of about 2 to about 8 and preferably about 2 to about 6.Other isocyanate-reactive materials which can be used in the presentinvention include hydrogen terminated polythioethers, polyamides,polyester amides, polycarbonates, polyacetals, polyolefins,polysiloxanes, and polymer polyols.

[0039] Suitable polyether polyols include reaction products of alkyleneoxides, e.g., ethylene oxide and/or propylene oxide, with initiatorscontaining from 2 to 8 active hydrogen atoms per molecule. Suitableinitiators include polyols, e.g., diethylene glycol, glycerol,trimethylolpropane, triethanolamine, pentaerythritol, sorbitol, methylglucoside, mannitol and sucrose; polyamines, e.g., ethylene diamine,toluene diamine, diaminodiphenylmethane and polymethylene polyphenylenepolyamines; amino alcohols, e.g., ethanolamine and diethanolamine; andmixtures thereof. Preferred initiators include polyols and polyamines.

[0040] Suitable polyester polyols include those prepared by reacting acarboxylic acid and/or a derivative thereof or a polycarboxylicanhydride with a polyhydric alcohol. The polycarboxylic acids may be anyof the known aliphatic, cycloaliphatic, aromatic, and/or heterocyclicpolycarboxylic acids and may be substituted, (e.g., with halogen atoms)and/or unsaturated. Examples of suitable polycarboxylic acids andanhydrides include oxalic acid, malonic acid, glutaric acid, pimelicacid, succinic acid, adipic acid, suberic acid, azelaic acid, sebacicacid, phthalic acid, isophthalic acid, terephthalic acid, trimelliticacid, trimellitic acid anhydride, pyromellitic dianhydride, phthalicacid anhydride, tetrahydrophthalic acid anhydride, hexahydrophthalicacid anhydride, endomethylene tetrahydrophthalic acid anhydride,glutaric acid anhydride acid, maleic acid, maleic acid anhydride,fumaric acid, and dimeric and trimeric fatty acids, such as those ofoleic acid which may be in admixture with monomeric fatty acids. Simpleesters of polycarboxylic acids may also be used such as terephthalicacid dimethylester, terephthalic acid bisglycol and extracts thereof.While the aromatic polyester polyols can be prepared from substantiallypure reactant materials as listed above, more complex ingredients may beadvantageously used, such as the side-streams, waste or scrap residuesfrom the manufacture of phthalic acid, phthalic anhydride, terephthalicacid, dimethyl terephthalate, polyethylene terephthalate, and the like.

[0041] The polyhydric alcohols suitable for the preparation of polyesterpolyols may be aliphatic, cycloaliphatic, aromatic, and/or heterocyclic.The polyhydric alcohols optionally may include substituents which areinert in the reaction, for example, chlorine and bromine substituents,and/or may be unsaturated. Suitable amino alcohols, such asmonoethanolamine, diethanolamine or the like may also be used. Examplesof suitable polyhydric alcohols include ethylene glycol, propyleneglycol, polyoxyalkylene glycols (such as diethylene glycol, polyethyleneglycol, dipropylene glycol and polypropylene glycol), glycerol andtrimethylolpropane.

[0042] The isocyanate-reactive material is used in an amount of about20% to about 70% and preferably about 30% to about 60% of the totalreaction system.

[0043] The present process further comprises reacting polyphenylenepolymethylene polyisocyanate composition (1) and isocyanate-reactivecomposition (2) with one or more hydrofluorocarbon or hydrocarbonblowing agents which are vaporizable under foam forming conditions. Thehydrofluorocarbon blowing agents useful in the present inventioninclude: 1,1,1,3,3-pentafluoropropane (HFC-245fa);1,1,1,3,3-pentafluorobutane (HFC 365mfc); 1,1,1,4,4,4-heptafluorobutane(IFC 356mff); 1,1-difluoroethane (HFC 152a), 1,1,1,2-tetrafluoroethane(HFC 134a) and mixtures thereof. Preferred hydrofluorocarbons include1,1,1,3,3-pentafluoropropane; 1,1,1,3,3-pentafluorobutane and1,1,1,2-tetrafluoroethane. Suitable hydrocarbons include butane,isobutane, isopentane, n-pentane, cyclopentane, 1-pentene, n-hexane,iso-hexane, 1-hexane, n-heptane, isoheptane, and mixtures thereof.Preferably the hydrocarbon blowing agent is isopentane, n-pentane,cyclopentane and mixtures thereof. The most preferred hydrocarbonblowing agent for use in the present invention is a blend of isopentaneto n-pentane in a ratio of 80:20 to 99:1 parts by weight.

[0044] The hydrofluorocarbon blowing agent should be used in an amountof about 2% to about 20% and preferably about 4 to about 15 percent ofthe entire reaction system.

[0045] The hydrocarbon blowing agent should be used in an amount ofabout 2% to about 20% and preferably about 4% to about 15% of the entirereaction system.

[0046] Other physical blowing agents may also be used in the presentprocess in combination with the hydrocarbon blowing agents. Suitableblowing agents include 1,1,1,3,3-pentafluoropropane (HFC-245fa),1,1,1,2-tetrafluorethane (HFC-134a), 1,1-difluoro ethane (HFC-152a),difluoromethane (HFC-32), chlorodifluoromethane (HCFC-22), and2-chloropropane. When used, these blowing agents may be mixed into theisocyanate-reactive component, the isocyanate component and/or as aseparate stream to the reaction system.

[0047] Vaporizable non-hydrofluorocarbons, such as 2-chloropropane,isopentane, cyclopentane may also be used in the present process incombination with the hydrofluorocarbon blowing agents. When used, theblowing agents may be mixed into the isocyanate-reactive component, theisocyanate component and/or as a separate stream to the reaction system.

[0048] The present process may optionally further comprise reacting thepolyphenylene polymethylene polyisocyanate, the isocyanate-reactivecomposition and the hydrofluorocarbon or hydrocarbon blowing agents inthe presence of water in an amount of 0.1% to about 5% and preferablyabout 0.2% to about 4% of the total reaction system. Water reacts togenerate carbon dioxide to act as an additional blowing agent. Othercarbon dioxide evolving compounds may further be used in place of or inaddition to water. Such compounds include carboxylic acids and cyclicamines.

[0049] The reaction system may further comprise one or more auxiliaryagents or additives as needed for one or more particular purposes.Suitable auxiliaries and additives include crosslinking agents, such astriethanolamine and glycerol; foam stabilizing agents or surfactants,such as siloxane-oxyalkylene copolymers and oxyethylene-oxyalkylenecopolymers; catalysts, such as tertiary amines, (e.g.,dimethylcyclohexylamine, pentamethyldiethylenetriamine,2,4,6-tris(dimethylaminomethyl) phenol, and triethylenediamine),organometallic compounds (e.g., potassium octoate, potassium acetate,dibutyl tin dilaurate), quaternary ammonium salts (e.g., 2-hydroxypropyltrimethylammonium formate) and N-substituted triazines (N,N′,N″-dimethylaminopropylhexahydrotriazine); flame retardants such asorgano-phosphorous compounds (such as organic phosphates, phosphites,phosphonate, polyphosphates, polyphosphites, polyphosphonate, ammoniumpolyphosphate (for example triethyl phosphate, diethy ethyl phosphonate,tris(2-chloropropyl)-phosphate) and halogenated compounds (such astetrabromophthalate esters, chlorinated parrafins); viscosity reducerssuch as propylene carbonate and 1-methyl-2-pyrrolidinone; infra-redopacifiers such as carbon black, titanium dioxide and metal flakes;cell-size reducing compounds, such as inert, insoluble fluorinatedcompounds and perfluorinated compounds; reinforcing agents, such asglass fibers and ground up foam waste; mold release agents, such as zincstearate; antioxidants, such as butylated hydroxy toluene; and pigmentssuch as azo-/diazo dyestuff and phthalocyanines. The amount of suchauxiliary materials or additives is generally between about 0.1 to about20%, preferably between about 0.3 to about 15% and most preferablybetween about 0.5 to about 10%, by weight based on 100% of the totalfoam formulation.

[0050] In operating the process for making rigid foams according to thisinvention, the known one-shot, prepolymer or semi-prepolymer techniquesmay be used together with conventional mixing methods, such asimpingement mixing. The rigid foam may be produced in the form ofslabstock, mouldings, cavity filling, sprayed foam, frothed foam orlaminates with other material such as paper, metal, plastics, orwood-board. See, e.g., Saunders and Frisch, Polyurethanes Chemistry andTechnology, Part II, Interscience Publishers, New York (1962), and thereferences cited for various methods of polyurethane formation.

[0051] The present invention further encompasses rigid polyurethanefoams produced by the processes disclosed above.

[0052] The present invention will now be illustrated by reference to thefollowing specific, non-limiting examples.

EXAMPLES

[0053] Unless otherwise noted, in the Examples set forth below, alltemperatures are expressed in degrees Celsius and amounts of allformulation components are expressed in parts by weight.

[0054] The following materials are used and referred to in the examples.

[0055] Stepanpol® PS-2352 is an aromatic polyester polyol available fromStepan Co. which comprises a phthalic anhydride/glycol-based (polyolhaving a hydroxyl value of 240 KOH/g and a viscosity of 3,000 cPs at 25°C.

[0056] TCPP is tri(beta-chloropropyl) phosphate available from GreatLakes Chemical Corporation.

[0057] Pelron® 9540A is potassium octoate in diethylene glycol availablefrom Pelron Corp.

[0058] Polycat® 8 is dimethyl cyclohexylamine available from AirProducts Corp.

[0059] Tegostab® B8466 is a silicone surfactant available fromGoldschmidt Corporation.

[0060] Borger Isopentane is an isopentane product containing 97.5%isopentane and 2.5% n-pentane available from Phillips Petroleum Company.

[0061] Hydrofluorocarbon HFC245fa (pressurized) available fromAlliedSignal.

[0062] Polyisocyanate A contained 32% of diphenyl methane diisocyanates,had a ratio of diisocyanate to triisocyanate of 1.2 (providing thetriisocyanate in an amount of 26.7%); and 41.3% of higher homologues.Isocyanate B had a diphenyl methane diisocyanate content of 44%; adiisocyanate to triisocyanate ratio of 1.8 (providing 24.4% oftriphenyldimethane triisocyanate); and 31.6% of higher homologues. BothIsocyanate A and B had an NCO content of 31%.

Example 1

[0063] A polyol blend was prepared by mixing 100 parts of StepanpolPS2352 with 14 parts of TCPP, 3 parts of Pelron 9540A. 0.6 parts ofPolycat 8, 2.65 parts of Tegostab B8466 and 1.3 parts of water in a highspeed mixer at room temperature.

[0064] Rigid foams were prepared from the formulations set forth inTable 1 below. The polyol blend was added to the ‘B side’ tank of anEdge-Sweets high pressure impingement mix dispense machine. Anappropriate amount of isopentane, based on the compositions set forth inTable 1, was then added to the ‘B side’ and mixed vigorously using anair-mixer attached to the tank. The isocyanate was then added to the ‘Aside’ tank attached to the dispense machine.

[0065] The machine parameters were set as follows: A side temperature (°F.) 70 B side temperature (° F.) 70 Mix pressure (psig) 2,000 A sidepump rpm 70 B side pump rpm adjusted to give appropriate isocyanateweight ratio as in Table 1 Dispense rate (g/sec) 180

[0066] The foaming ingredients were shot from the dispense machine into#10 Lily cup and reactivity was measured on free use foam.

[0067] The structural properties were measured on core specimens takenfrom 7″×7″×15″ foams made by dispensing foam ingredients into anappropriate cardboard box.

[0068] Foam core density was measured according to ASTM D1622. The hightemperature dimensional stability was measured following ATM D2126. Thecompressive strength was measured parallel and perpendicular to foamrise direction according to ASTM D1621 Procedure A. The thermalproperties of the foams were measured according to ASTM C518 on corefoam taken from 2″×14″×14″ blocks. Fire performance was tested accordingto ASTM D3014 to measure Butler Chimney weight retention. TABLE 1 FoamFoam Foam Foam #1 #2 #3 #4 ′B-side′ Polyol Blend 34.8 34.8 34.5 34.5Isopentane 6.2 6.2 6.6 6.6 ′A-side′ Isocyanate A 59 — 58.9 — IsocyanateB — 59 — 58.9 Isopentane Reactivities: Cream Time, seconds 4 5 6 5 GelTime, seconds 24 24 24 26 Tack-Free Time, seconds 42 43 62 51 FoamProperties: 1.9 1.9 1.75 1.75 Core Density, pcf Structural Properties:Dimensional stability, % linear change 7 days at −25° C. −1 −2.9 −1.9−3.6 7 days at 93° C./amb 2 2.6 2.7 3.4 7 days at 70° C./97% RH 2.2 3.43.5 3.6 Compressive Strength, psi Parallel to rise 39.4 34.3 37.6 33.3Perpendicular to rise 12.3 8.8 11.3 11.1 Thermal Properties: k-factor inBTU. in/ft². hr. ° F. Initial 0.15 0.15 0.15 0.15 After 8 wks at 140° F.0.17 0.18 0.18 0.18 Fire Properties: 93 88 88 86 Butler Chimney, % wt.retained

[0069] It can be clearly seen from the data set forth in Table 1, thatFoam 1 prepared with Isocyanate A according to the present inventionprovides a rigid polyurethane foam which is superior in structural,thermal and fire performance properties in comparison to Foam 2. Foam 2was prepared with Isocyanate B which is outside the scope of the presentinvention.

[0070] Foams 3 and 4 were prepared at densities typical of CFC blownfoam. As set forth in Table 1, Foam 3 prepared with Isocyanate A,according to the present invention, has superior structural thermal andfire performance properties in comparison to Foam 4. Foam 4 was preparedwith Isocyanate B which is outside the scope of the present invention.

[0071] Moreover, Foam 3 (according to the present invention) can becompared to Foam 2. The dimensional stability and Butler chimney weightretention are nearly identical for the two foams. Also, the compressionstrength, along with the initial and aged K factors of Foam 3 aresuperior to those for Foam 2. Accordingly, the data demonstrates thatfoams prepared with a polyisocyanate composition according to thepresent invention (Isocyanate A) have better performance properties atlower densities that those of foam prepared with conventionalisocyanates at higher densities.

Example 2

[0072] A polyol blend was prepared by mixing 100 parts of StepanpolPS2352 with 4.5 parts of Pelron 9540A. 1.0 parts of Polycat 8, 2.0 partsof Tegostab B8466 and 0.3 parts of water in a high speed mixer at roomtemperature.

[0073] Rigid foams were prepared from the formulations set forth inTable 1 below. The polyol blend was added to the ‘B side’ tank of anEdge-Sweets high pressure impingement mix dispense machine. Anappropriate amount of HFC245fa, based on the compositions set forth inTable 1, was then added to the ‘B side’ and mixed vigorously using anair-mixer attached to the tank. The isocyanate was then added to the ‘Aside’ tank attached to the dispense machine.

[0074] The machine parameters were set as follows: A side temperature (°F.) 70 B side temperature (° F.) 70 Mix pressure (psig) 2,000 A sidepump rpm 70 B side pump rpm adjusted to give appropriate isocyanateweight ratio as in Table 1 Dispense rate (g/sec) 200

[0075] The foaming ingredients were shot from the dispense machine into#10 Lily cup and reactivity was measured on this free rise foam.

[0076] The structural properties were measured on core specimens takenfrom 7″×7″×15″ foams made by dispensing foam ingredients into anappropriate cardboard box.

[0077] Foam core density was measured according to ASTM D1622. The hightemperature dimensional stability was measured following ATM D2126. Thecompressive strength was measured parallel and perpendicular to foamrise direction according to ASTM D1621 Procedure A. The thermalproperties of the foams were measured according to ASTM DC518 on corefoam taken from 2″×14″×14″ blocks. Fire performance was tested accordingto ASTM D3014 to measure Butler Chimney weight retention. TABLE 1 FoamFoam Foam Foam #1 #2 #3 #4 ′B-side′ Polyol Blend 34.4 34.4 34.0 34.0HFC245fa 13.7 13.7 14.6 14.6 ′A-side′ Isocyanate A 51.9 — 58.4 —Isocyanate B — 51.9 — 58.4 Reactivities: Cream Time, seconds 3 3 3 3 GelTime, seconds 11 11 11 11 Tack-Free Time, seconds 15 14 13 13 FoamProperties: 2.14 2.14 2.02 2.02 Core Density, pcf Structural Properties:Dimensional stability, % linear change 7 days at −25° C. −1.1 −3.6 −1.3−5.2 7 days at 93° C./amb 2.3 4.4 3.6 5 Compressive Strength, psiParallel to rise 47.9 34 40.2 32 Perpendicular to rise 21.3 11.5 13.910.8 Thermal Properties: 0.128 0.132 0.129 0.130 k-factor in BTU.in/ft². hr. ° F. Initial

[0078] It can be clearly seen from the data set forth in Table 1, thatFoam 1, prepared with Isocyanate A according to the present invention,provides a rigid polyurethane foam which is superior in structural,thermal and fire performance properties in comparison to Foam 2. Foam 2was prepared with Isocyanate B which is outside the scope of the presentinvention.

[0079] Foams 3 and 4 were prepared at densities typical of CFC blownfoam. As set forth in Table 1, Foam 3, prepared with Isocyanate Aaccording to the present invention, has superior structural thermal andfire performance properties in comparison to Foam 4. Foam 4 was preparedwith Isocyanate B which is outside the scope of the present invention.

[0080] Moreover, Foam 3 (according to the present invention) can becompared to Foam 2. The dimensional stability value is nearly identicalfor the two foams. Also, the compressive strength, along with theinitial and aged K factors of Foam 3 are superior to those for Foam 2.Accordingly, the data demonstrates that foams prepared with apolyisocyanate composition according to the present invention havebetter performance properties at lower densities that those of foamprepared with conventional isocyanates at higher densities.

What is claimed is:
 1. A polyisocyanate composition comprising: (a) fromabout 15 to about 42 percent by weight of diphenylmethane diisocyanate,(b) three ring oligomers of polyphenylene polymethylene polyisocyanatein an amount such that the ratio of (a) to (b) is equal to from about0.2 to about 1.8, and (c) higher homologues of polyphenylenepolymethylene polyisocyanate.
 2. A composition as claimed in claim 1,wherein the three ring oligomers of polyphenylene polymethylenepolyisocyanate have the following formula:

wherein n=1.
 3. A composition as claimed in claim 1 wherein the higherhomologues of polyphenylene polymethylene polyisocyanate have thefollowing formula:

wherein n>1.
 4. A composition as claimed in claim 1 wherein the amountof diphenylmethane diisocyanate is equal to from about 20 to about 40percent.
 5. A composition as claimed in claim 1 wherein the amount ofdiphenylmethane diisocyanate is equal to from about 24 to about 38percent.
 6. A process for preparing a polyurethane foam, said processcomprising reacting a polyisocyanate composition as claimed in claim 1with an isocyanate reactive composition in the presence of ahydrofluorocarbon blowing agent.
 7. A process as claimed in claim 6wherein the amount of hydrofluorocarbon is equal to from about 2% toabout 20% by weight of the composition.
 8. A process as claimed in claim6 wherein the amount of hydrofluorocarbon is equal to from about 4% toabut 15% by weight of the composition.
 9. A process as claimed in claim7 wherein the hydrofluorocarbon is selected from the group consisting of1,1,1,3,3-pentafluoropropane (HFC-245fa); 1,1,1,3,3-pentafluorobutane(HFC 365mfc); 1,1,1,4,4,4-heptafluorobutane (HFC 356mff);1,1-difluoroethane (HFC 152a), 1,1,1,2-tetrafluoroethane (HFC 134a) andmixtures thereof.
 10. A process for preparing a polyurethane foam, saidprocess comprising reacting a polyisocyanate composition as claimed inclaim 1 with an isocyanate reactive composition in the presence of ahydrocarbon blowing agent.
 11. A process as claimed in claim 10 whereinthe amount of hydrocarbon is equal to from about 2% to about 20% byweight of the composition.
 12. A process as claimed in claim 10 whereinthe amount of hydrocarbon is equal to from about 4% to about 15% byweight of the composition.
 13. A process as claimed in claim 10 whereinthe hydrocarbon is selected from the group consisting of butane,isobutane, isopentane, n-pentane, cyclopentane, 1-pentene, n-hextane,iso-hexane, 1-hexane, n-heptane, isoheptane, and mixtures thereof.
 14. Aprocess as claimed in claim 10 wherein the hydrocarbon is a blend ofisopentane to n-pentane in a ratio of 80:20 to 99:1 parts by weight.